1. Field of the Invention
The invention relates generally to an intake structure for an internal combustion engine, and more specifically to an intake structure for an internal combustion engine, which includes a valve that controls the airflow.
2. Description of the Related Art
Technologies relating to an intake structure for an internal combustion engine have been developed. For example, Japanese Patent Application Publication No. 2004-124836 (JP-A-2004-124836) describes an air-intake apparatus for an internal combustion engine, which is designed to allow the gas to flow more efficiently in a cylinder without excessively reducing the opening ratio at an intake port. According to Japanese Patent Application Publication No. 2004-124836 (JP-A-2004-124836), an intake-air control valve that produces gas flows such as a tumble flow and a swirl flow in the cylinder is provided in the intake port. The intake-air control valve includes a rotating shaft connected to an actuator, and a flat plate-like valve element that is supported, at one end thereof, by the rotating shaft. When the intake-air control valve is at the opening position, the intake-air control valve is housed in a recess formed in a lower portion of the inner face of the intake port.
According to the aforementioned Japanese Patent Application Publication No. 2004-124836 (JP-A-2004-124836), when being at the opening position, the intake-air control valve is housed in the recess formed in the intake port to suppress the hindrance to the airflow in the intake port. However, if oil, fuel, water, etc. contained in the intake air accumulate in the recess, the deposits may interfere with the rotation of the rotating shaft of the intake-air control valve. This may hinder the smooth operation of the intake-air control valve, or increases the load placed on the actuator due to an increase in the torque required to operate the intake-air control valve.